> Yes, some make use of Thread-id a bit better than other
Traditional email threading was based on the contents of the In-Reply-To and References headers. The algorithm is described in RFC 5256 for the IMAP SORT and THREAD extensions[1] and used in several mail user agents[2].
Traditional email threading was based on the contents of the In-Reply-To and References headers. The algorithm is described in RFC 5256 for the IMAP SORT and THREAD extensions[1] and used in several mail user agents[2].
[1] https://tools.ietf.org/html/rfc5256#ref-THREADING
[2] https://www.jwz.org/doc/threading.html